1. Field of the Invention
The present invention relates to a photosensitive composition which causes reaction by irradiation with an actinic ray or a radiation, whereby its property changes. In more detail, the invention relates to a resist composition to be used in the manufacturing step of semiconductors such as IC, the manufacture of circuit boards such as liquid crystals and thermal heads, and other fabrication steps.
2. Description of the Related Art
A chemically amplified resist composition is a pattern forming material of forming an acid in an exposed area by irradiation with the radiation such as far ultraviolet light and changing the solubility in a developer between the actinic ray-irradiated area and the non-irradiated area due to a reaction using the formed acid as a catalyst, to form a pattern on a substrate.
In the case where a KrF excimer laser is an exposure light source, since a resin comprising as a basic skeleton poly (hydroxystyrene) exhibiting low absorption mainly in a region of 248 nm is used as the major component, this chemically amplified system is able to form a good pattern at high sensitivity and high resolution and is a good system as compared with a conventional naphthoquinonediazide/novolak resin system.
On the other hand, in the case where a light source having a shorter wavelength, for example, an ArF excimer laser (193 nm), is used as an exposure light source, since an aromatic group-containing compound exhibits high absorption substantially in a region of 193 nm, even the foregoing chemically amplified system was not satisfactory yet.
For this reason, a resist for ArF excimer laser containing a resin having an alicyclic hydrocarbon structure has been developed.
With respect to an acid generating agent which is the major constitutional component of a chemically amplified resist, a variety of compounds have been found. JP-A-9-309874 describes a positive photosensitive composition containing a divalent arylsulfonic acid sulfonium salt or iodonium salt.
However, performances such as an exposure margin in which the performance changes due to a fine change of the exposure amount and density dependency in which the performance changes due to the pattern density such as a dense pattern and an isolated pattern are not satisfactory yet, and therefore, improvements have been demanded.
Also, in a resin having an alicyclic hydrocarbon structure, the system becomes extremely hydrophobic as an evil influence of the alicyclic hydrocarbon structure. Therefore, development with a tetramethylammonium hydroxide (herein-after referred to as “TMAH”) aqueous solution that has hitherto been widely used as a resist developer becomes difficult. Also, there is observed a phenomenon in which a resist peels away from a substrate during the development.
For example, JP-A-9-73173 and JP-A-10-161313 describe resist materials using an acid sensitive compound containing an alkali-soluble group protected by an alicyclic group-containing structure and a structural unit such that the alkali-soluble group is eliminated by an acid, thereby making the compound alkali-soluble. These materials are of an excellent design from which a hydrophilic/hydrophobic contrast is obtained because the structure containing a hydrophobic alicyclic group is eliminated. However, these materials were not satisfactory yet with respect to the developability with a TMAH aqueous solution and peeling of a resist from a substrate during the development. For this reason, there have been various investigations with respect to the introduction of a hydrophilic group into a resin having an alicyclic hydrocarbon site introduced thereinto.
Japanese Patent No. 2,776,273 and JP-A-11-109632 describe the use of a resin containing a polar group-containing alicyclic functional group and an acid decomposable group in a radiation sensitive material.
Also, JP-A-9-90637, JP-A-10-207069, JP-A-10-274852, JP-A-2001-188351, and Japanese Patent No. 3,042,618 describe photoresist compositions containing a polymer obtained by copolymerizing a (meth)acrylate derivative having a lactone structure with other polymerizable compound.
Also, JP-A-2001-109154, JP-A-2000-137327, JP-A-2002-296783, and JP-A-2001-215704 describe positive working photoresist compositions containing a copolymer resin of the foregoing lactone monomer and a monomer having a hydroxyadamantane structure as a polar group-containing alicyclic functional group.
As described previously, though there have been investigated a variety of measures for improving the hydrophobicity of the resin, the foregoing techniques involve a lot of unsatisfactory points, and improvements are desired. In particular, in forming a fine pattern with a line width of not more than 100 nm, it is required that a resist composition does not depend upon the coverage of a mask (rate of an exposed area to an unexposed area) or the pitch of a pattern, i.e., the presence of pattern density, and is hardly influenced by a change of the pattern forming condition (exposure amount and focus) (that is, the process window is wide). However, in the foregoing compositions, there was still room for improvements regarding the process window.
Also, in the resist for ArF excimer laser containing a resin having an alicyclic hydrocarbon structure, there was encountered such a problem that in forming a fine pattern with a line width of not more than 100 nm, the resist pattern collapses so that the subsequent processing of a substrate by dry etching cannot be achieved. This problem becomes remarkable as the processed line width becomes fine. Thus, a resist capable of forming a fine pattern without causing collapse is demanded.
Also, under the circumstance where it is necessary to form a fine pattern with a line width of not more than 100 nm, in particular, in forming an isolated pattern, it becomes difficult to ensure the focus latitude, i.e., the depth of focus (DOF). Thus, a resist composition having a wider DOF performance is demanded.
In forming a resist pattern from a resist composition, the composition is in general used upon dissolution in a proper solvent. In this regard, the precision, resolution, etc. of the resulting resist pattern are also largely influenced by the kind or combination of the solvent to be used in forming a resist pattern. Moreover, when the composition in the solution state is coated (especially, rotary coated) on a substrate, there was a problem that the surface of the coated resist film is not always satisfactorily uniform so that the uniformity in film thickness is not satisfactory.
Hitherto, for the solution of a chemical amplification type radiation sensitive composition, various solvents such as ethers, glycol ethers, glycol ether acetates, cellosolve esters, aromatic hydrocarbons, ketones, and esters have been used, and their kinds include many different materials. Also, the characteristics of the resist pattern are closely related to the composition to be used.
For example, JP-A-10-254139 describes a radiation sensitive resin composition comprising (A) an alkali-insoluble or sparingly alkali-soluble acid-cleavable group-containing resin having an alicyclic skeleton in the principal chain and/or the side chain, the resin becoming alkali-soluble upon cleavage of the acid-cleavable group, (B) a radiation sensitive acid generating agent capable of generating an acid by irradiation with the radiation, and (C) a solvent comprising a mixture of a cyclic ketone or at least one kind selected from the group consisting of propylene glycol monoalkyl ether acetates and alkyl 2-hydroxypropionates and a linear ketone, the radiation sensitive resin composition being excellent with respect to transparency against the radiation, dry etching resistance, uniformity in film thickness, adhesion to a substrate, sensitivity, resolution, developability, and the like.
Also, JP-A-2000-241964 describes that a photoresist composition containing a ketone based solvent such as cyclohexanone, isobutyl methyl ketone, 2-heptanone, 3-heptanone, 4-heptanone, cyclopentanone, 2-methylcyclopentanone, 3-methylcyclopentanone, 2-methylcyclohexanone, 3-methylcyclohexanone, and 2,4-dimethylpentanone exhibits shear thinning property and that even in an atmosphere where an amine in a high concentration is present, an excellent photoresist fine pattern can be obtained without adding another step for the removal of the amine, whereby a reduction of the costs can be achieved.
However, the application range of the contents disclosed in these documents is not always wide, and it is the actual situation that it is quite difficult to find out an adequate solvent or combinations thereof corresponding to the composition containing a resin, a photo acid generating agent, additives, and the like from the viewpoint of the overall performance as a resist. Further, in forming a fine pattern with a line width of not more than 100 nm, improvements in the defocus latitude performances regarding the prevention from pattern collapse and isolated line pattern of the resist were still demanded.